Welcome to the ESID 2022 Meeting Interactive Programme
The meeting will officially run on Central European Summer Time (CEST)
Introduction
B Cell Tolerance Checkpoints
Mechanisms of T cell Tolerance
PIK3CD GOF Breaches B Cell Tolerance Checkpoints
IMMUNE TOLERANCE DEFECTS IN INDIVIDUALS WITH PATHOGENIC MUTATIONS IN THE KAPPA LIGHT CHAIN
Abstract
Background and Aims
Germline homozygous or compound heterozygous mutations in the gene encoding the constant domain of the immunoglobulin κ light chain (IGKC) may cause kappa light deficiency. Only few cases have been reported since its first characterisation, with very variable susceptibility to infections. κ light chain expression is involved in the process of B cell receptor (BCR) editing, a pivotal autoimmune checkpoint. Thus, IGKC mutations might predispose to autoimmunity.
Methods
We screened our inborn errors of immunity cohort consisting of 360 patients by Sanger sequencing for rare IGKC mutations. In addition, we screened 490 individuals of the Swiss SLE Cohort Study and are currently screening 500 patients enrolled into a Swiss Rheumatoid Arthritis cohort. IGKC mutation carriers were characterised clinically. We comprehensively evaluated the immune-phenotype including κ vs λ light chain expression on B cell subpopulations by flow-cytometry.
Results
So far, we have identified five individuals carrying the heterozygous c.T258G mutation in IGKC. This mutation changes an essential cysteine involved in disulphide bonds. Only one mutation carrier had kappa light chain deficiency in the serum. However, all expressed predominantly λ light chains on the surface of peripheral B cells implicating pathologic receptor editing. All mutation carriers had autoimmune disease, which in the majority was life-threatening.
Conclusions
We present evidence that the c.T258G IGKC missense variant in heterozygous state disturbs B cell receptor editing with high penetrance. The clinical associations found indicate a considerable penetrance of the c.T258G IGKC mutation to drive human autoimmune disease.
HYPERMORPHIC HETEROZYGOUS VARIANTS IN ZAP70 UNDERLIE AUTOIMMUNE DISEASE
Abstract
Background and Aims
The tyrosine kinase ZAP-70 plays a crucial role in relaying proximal T cell antigen receptor signalling. Biallelic loss-of-function mutations in ZAP70 consequently cause a severe combined immunodeficiency with defective CD4+ T cell functioning and CD8+ T cell lymphopenia. Moreover, there has been a report of a ZAP70 variant (p.Arg360Pro) conferring a weak hypermorphic effect in two siblings with autoimmune disease, although not fully penetrant. In this study, we have investigated the functional impact of two novel heterozygous missense variants in ZAP70 carried by six patients with multiple autoimmune diseases.
Methods
An exome-wide research-based reanalysis was performed in three unrelated index patients. Segregation of rare, non-synonymous candidate genes in affected family members was investigated using Sanger sequencing. Functional tests were conducted to test pathogenicity and encompassed ex vivo stimulation of isolated peripheral blood mononuclear cells, ELISA for cytokine production and phosphoflow cytometry analysis.
Results
In index patients 1 and 2, an identical heterozygous missense variant (p.(Leu325Phe)) was identified. Index patient 3 carried another, private heterozygous missense variant (p.(Val114Phe)). All variants showed complete segregation in affected family members. An increased basal phosphorylation of ZAP70 was observed in PBMCs isolated from the patients, suggesting a compromised autoinhibitory state. Furthermore, in patients with the p.Leu325Phe variant, basal IFNgamma production and T cell activation after TCR stimulation were also elevated compared to controls.
Conclusions
In patients from three families with autoimmune disease, we identified rare, heterozygous missense variants in ZAP70. These hypermorphic variants led to increased basal ZAP-70 phosphorylation and augmented T-cell signalling, suggesting a novel mutational mechanism.